1. Field of the Invention
The present patent application for industrial invention relates to an absolute angular and/or linear encoder based on a capacitative coupling principle. Such an encoder is able to send information on the angular and/or linear position of a mobile element to an electronic device, such as a display that displays such information on the position.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98
It is often necessary to have information on the angular and linear position of a mobile element (for example a knob with an integrated button). It is also possible to transmit the information on the angular and linear position in order to be used by another system.
Position transducer devices with similar characteristics are typically used in household appliances, and also in other applications.
Said position transducer devices comprise a shaft that can be rotated either manually or by means of a motor to generate an electrical signal. The electrical signal generated by the device can be a resistance value or a sequence or electronic configuration of bits. The term “potentiometric device” can be used when the output of the detection device is a resistance value, whereas the term “encoder” is used alternatively.
An encoder comprises three main parts: an electronic printed circuit board (PCB), a rotor and a shaft. Various parts are generally assembled on the PCB, such as: resistive devices, microcontrollers, capacitors, conductive tracks, carbon film tracks and other devices. Encoders generally use mechanical rotary friction contacts between the rotor and the PCB to produce an electronic signal that corresponds to each angular position of the rotor.
Relative or incremental encoders as well as absolute encoders are known.
In relative encoders the electrical output signals are proportional to the displacement of the rotor with respect to a fixed reference point. Simple circuits can read and display the speed and acceleration of the rotor axis, but not the instantaneous position.
In absolute encoders the electrical output signals encode the exact instantaneous position of the rotor with respect to a fixed reference point. In such a way, at any time, a suitable decoding circuit can decode and display the angular position of the rotor axis. The displacement data of the axis (direction, speed and acceleration) are obtained processing its absolute position in time.
The following devices are known:                resistive potentiometers and absolute angular and linear encoders with mechanical rotary friction contacts,        absolute or incremental optical angular encoders,        absolute or incremental magnetic angular encoders,        incremental capacitative angular encoders.        
Nevertheless the aforementioned devices are impaired by the following drawbacks:                resistive or rotary contact encoders/potentiometers are subject to rapid wear of the contact elements, which are necessarily of friction type, and have large dimensions (which are difficult to miniaturize) in the direction of the rotor axis of rotation.        
The dimensions of the optical encoders are difficult to miniaturize in the direction of the rotor axis of rotation.
Capacitative encoders are only used as incremental, not absolute encoders. In fact, the armatures used to detect the rotation of the rotor cannot be used to detect also the distance of the rotor from the stator. Moreover, the stator and rotor armatures of capacitive encoders must be electrically connected to the measuring and control electronics.
US2009/0064809 discloses a rotary knob assembly provided with a stator with a plurality of conductive sectors disposed in linear arrangement that form armatures of capacitors and small conductive cursors mounted in peripheral position in the knob to generate a capacity variation in the stator capacitors.
US2006/0012944 discloses a mechanically operable electrical device comprising capacitor armatures disposed in circumferential arrangement in a stator and a rotary element provided with a small radial conductive region to generate a capacity variation in the stator capacitors.
EP0920042 discloses an apparatus panel comprising a plurality of capacitor armatures disposed in circumferential arrangement in a stator and a rotary element with a conductive indicator that extends radially from the rotary element to generate a capacity variation in the stator capacitors.
US2009/0064809, US2006/0012944 and EP0920042 disclose a rotary element provided with a conductive section with a considerably lower surface compared to the non-conductive section of the rotary element. The conductive section of the rotary element has basically the same dimensions as a single stator armature. Consequently, the capacity variation of a single stator armature is analyzed upon the passage of the conductive cursor. In view of the above, only one stator armature affects the calculation of the capacity variation, whereas no contribution is given by the other stator armatures. This clearly involves evident resolution limits.
In order to partially solve such a drawback, US2006/0012944 and EP0920042 teach to ground the conductive section of the rotor in order to screen the stator armature covered by the conductive section of the rotor with respect to the other stator armatures. Evidently, the ground connection of a rotary element is complicated and not very reliable.
The purpose of the present invention is to eliminate the drawbacks of the prior art by providing a capacitative encoder able to detect with capacitative measures the absolute angular and linear position of the mobile element of the encoder not electrically connected to the measuring and control electronics.
Another purpose of the present invention is to provide a rotary encoder that is reliable and easy to make.
A further purpose of the present invention is to provide a rotary encoder that is suitable for being used as knob that provides for both rotation and translation.